1. P.K. Lin 1

2. Outline Introduction Experiments Results and Discussion Conclusion
References 2

3. Introduction
Over the past few years, people have proposed numerous physics mechanisms to explain the phenomenon of efficiency droop, such as Auger recombination ,electron leakage , poor hole injection efficiency , polarization effect , and the quantum confined stark effect.
Up to now, however, the approaches to improve efficiency droop are still mainly to suppress the electron overflow, enhance the hole injection efficiency, and reduce the polarization field. 3

4. Introduction
Such as the usage of staggered quantum wells (QWs) ,AlGaN barriers , indium graded last barrier , p-InGaN hole reservoir layer , graded electron blocking layer (EBL) , and AlGaN/GaN superlattice EBL of gradual Al mole fraction.
In this paper, the idea of InGaN barriers and dip-shaped last barrier is proposed with reduced polarization effect, decreased electron current overflow, and increased hole injection efficiency. 4

5. Experiments The structue of the conventional (Original structure)
C-plan Sapphire
2um-undoped GaN Layer
2μm Si-doped N-GaN(n = 5 x1018cm-3)
MQW
20nm Al0.15Ga0.85NEBL (p = 5x1017cm-3)
170nm Mg-doped P-GaN (p = 7x1017cm-3)
N contact
ITO
P contact
The structue of the conventional (Original structure)
LED
MQW
Composition
In0.16Ga0.84N/ GaN
Pair
six-period
Thickness
3nm/10nm
Chip size: 300x300(um2) 5

6. FIG. 1. Schematic view of InGaN LEDs with conventional GaN barrier
(original structure), InGaN barriers (structure A), and InGaN barriers and
dip-shaped last barrier (structure B). 6

7. Results and Discussion
At 200mA
Efficiency droop
Original structure
40.9%
Structure A
27.7%
Structure B
23.5%
Fig (a) Light output power, (b) I –V curves, and (c) IQE for the three LEDs. 7

8. Fig. 3. Electrostatic fields and band wavefunctions of the three LEDs at
200 mA. 8

9. Fig. 4. Energy band diagrams of the three LEDs at 200 mA.9

10. Fig (a) Electron concentrations, (b) hole concentrations,and (c) electron current density of the three structures at 200 mA. 10

11. Fig. 6. Radiative recombination rate inset with spontaneous emission rate
of the three structures at 200 mA. 11

12. Conclusion
In summary, it is found that the electron leakage is markedly reduced, the hole injection efficiency is greatly enhanced.
In addition, the electrostatic fields in the MQWs are relieved effectively when the conventional GaN barriers are replaced by InGaN barriers and dip-shaped last InGaN barrier .
Therefore, the optical and electrical performances of the newly designed LED acquired a significant improvement. 12

13. References
R.M.Lin,S.F.Yu,S.J.Chang, T.H.Chiang,S.P.Chang,andC.H. Chen, “Inserting a p-InGaN layer before the p-AlGaN electron blocking layer suppresses efficiency droop in InGaN-based light-emitting diodes,” Appl. Phys. Lett., vol.101,no.8,pp – ,Aug.2012.
T.Lu,S.Li,C.Liu,K.Zhang,Y.Xu,J.Tong,L.Wu,H.Wang, X.Yang,Y.Yin,G.Xiao,andY.Zhou,“Advantages of GaN basedlight-emitting diodes with a p-InGaN hole reservoir layer,” Appl. Phys. Lett.,vol.100,no.14,pp – ,Apr.2012.
C.S.Xia,Z.M.Simon Li,W.Lu,Z.H.Zhang,and L.W.Cheng,“Droop improvement in blue InGaN/GaN multiple quantum well light-emitting diodes with indium graded last barrier,”Appl. Phys. Lett.,vol.99,no.23,pp – , Dec 13

14. Thanks for your attention!

15. References

16. SRH recombination lifetime Operating temperature
The advanced physical model of semiconductor devices simulation software
The key parameters
Set on
The radiative
2.0 x cm3/s
Internal absorption
2000m-1
Auger cofficients
1.0 x cm3/s
SRH recombination lifetime
100ns
Operating temperature
300K

19. References

20. My Designed EBL structure of LED
p-AlGaN
Original structure
MQW(GaN/InGaN)
n-GaN
p-GaN
p-AlGaN
New structure
p-GaN
MQW(GaN/InGaN)
n-GaN
透過在MQW與EBL間插入一層AlGaN superlattice ，做為緩衝last barrier 與EBL lattice mismatch 所帶來能帶傾斜的效應!!進而增加EBL有效的能障高度…

21. My Designed EBL structure
p-GaN
n-GaN
p-AlGaN
MQW(GaN/InGaN)
Original structure
n-GaN
New structure
p-GaN
p-type
n-type
在last barrier 做一n參雜，目的在於 行程一空乏區內建電場!透過PN面 空乏區電場來去抵補極化場!!

22. 極化場方向
內建電場方向

24. My Designed EBL structure
n-GaN
New structure
p-GaN
p-type
n-type
n-type EBL
p-type EBL
p-type GaN barrier
p-GaN